1. Field of the Invention
The invention relates to a sewing machine with an overload clutch for breaking the drive connection when a blockage occurs.
2. Related Art
A known sewing machine with an overload clutch is the ADLER Model 167-FA3S, which is described in the replacement parts diagram designated xe2x80x9cAdler 167-3S; -FA3S, TL. 402 167-24.2-Nov. 1979.xe2x80x9d In this sewing machine, the overload clutch, capable of being engaged in a predetermined position, is provided between the handwheel, designed as a driving wheel, and the arm shaft which functions as the drive shaft of the sewing machine.
One disadvantage of this sewing machine is that, if there is a blockage and the overload clutch is disengaged as a result, impact loads, that is to say a moment of momentum, are continuously exerted on the blocked sewing machine in the course of each revolution of the driving part while the sewing machine drive is in the run-down phase. This results in a considerable load on the components involved. Moreover, the duration of this load depends on how quickly the operator of the sewing machine notices the blockage and causes the sewing machine to stop by actuating the pedal appropriately.
Further, the assembly and adjustment of the known sewing machine take a considerable amount of time, especially the adjustment of the setscrews (part no. 992 01 231 0 in the above-mentioned replacement parts diagram) which set the springs (067 35 008 0) so that the springs apply a relatively uniform prestressing force of a desired magnitude to the positioning balls (996 06 025 0) in the overload clutch.
The invention provides an improved sewing machine with an overload clutch, wherein it becomes easier for the operator to work on the sewing machine, the behavior of the operator no longer has any influence in the event of a fault, and the load on the sewing machine when a blockage occurs is reduced.
This object may be achieved, according to one aspect of the invention, by a sewing machine with the following features:
a drive shaft with a driving wheel,
a drive motor with an electronic control, the drive motor being drivingly connected to the driving wheel,
a position transmitter transmits signals to the control representing the rotary position of the drive shaft, the position transmitter being connected to the drive shaft for being driven thereby, and
the position transmitter""s signals to the control indicate when a blockage on the sewing machine occurs, whereupon the control causes the drive motor to stop.
Advantageously, the overload clutch is a friction clutch and is arranged between the driving wheel and the drive shaft.
What is achieved according to this aspect of the invention is that, when the overload clutch takes effect, impact loads on the sewing machine are basically eliminated, and the drive motor is stopped automatically if a blockage occurs, irrespective of the operator""s behavior. With the sewing machine according to the invention, handling becomes easier, wear on components of the sewing machine is reduced and a reliably working solution which can be produced at lower cost is provided.
An advantageous development is proposed by the feature wherein the driving wheel is designed with a handwheel.
The feature wherein the overload friction clutch has a single pair of frictional surfaces, the pressure force of which is applied by a prestressed spring, leads to a very simple and cost-effective solution. The value of the transmittable torque can easily be set, since the prestress of the spring can be set by means of a nut. This makes it possible to adapt to the respective type of sewing machine and its load and to limit the load which is applied to the machine parts of the sewing machine in the event of faults.
Other features and advantages of the present invention will become apparent from the following description of an embodiment of the invention which refers to the accompanying drawings.